Conventionally, some internal combustion engines for vehicles are equipped with an exhaust turbine supercharger (so-called turbocharger) to obtain high power. Generally, an exhaust turbine supercharger has the following construction. An exhaust turbine is provided within an exhaust pipe of the internal combustion engine and is connected to a compressor provided on an intake pipe. Kinetic energy of exhaust gas is used to rotatively drive the exhaust turbine. In this manner, the compressor is rotatively driven to supply intake air.
The technology to control boost pressures of the supercharged internal combustion engine is described in JP-A-1995-332097 as follows, for example. A waste gate valve is provided on an exhaust bypass pipe that bypasses an exhaust turbine. A boost pressure sensor detects a boost pressure that should match a target boost pressure. For this purpose, the waste gate valve opening is feedback-controlled to control the amount of exhaust gas supplied to the exhaust turbine. This controls rotational speeds of the exhaust turbine and the compressor to control boost pressures.
Japanese Patent No. 2528384 describes a supercharged internal combustion engine as follows. A boost pressure sensor detects boost pressures. Based on the boost pressures, the supercharged internal combustion engine corrects the intake air amount detected by an air flow meter. This improves the detection accuracy of the intake air amount during supercharging.
JP-A-2002-180889 describes a supercharged internal combustion engine as follows. The super charged internal combustion engine calculates intake temperatures after supercharging using a map and the like. The calculation is based on an intake temperature and an intake pressure (atmospheric pressure) before supercharging and a boost pressure detected by a boost pressure.
However, the above-mentioned conventional technologies control boost pressures based on detection values for the boost pressure sensor. Alternatively, the technologies calculate intake air amounts and intake temperatures based on detection values from the boost pressure sensor. Depending on cases, the boost pressure sensor may fail or degrade the detection accuracy. Under such usage environment or operating conditions, it is necessary to inhibit control or processes based on detection values from the boost pressure sensor. It becomes impossible to provide control or processes based on boost pressures. Since the boost pressure sensor must be always provided, the number of parts increases to increase costs.